A mixer is an apparatus which converts an incoming signal from one frequency to another by combining it with a local oscillator signal in a non-linear device such as a diode. Mixers are often used in radar systems to convert an incoming radio frequency (RF) (from a target) to a lower intermediate frequency (IF) before further processing. In general, mixing produces a large number of sum and difference frequencies. Usually the difference frequency between the signal (RF frequency) and local oscillator (LO frequency) is of interest.
Usually the LO frequency is close to the RF frequency. A subharmonic mixer utilizes an LO frequency which is approximately one-half of the RF frequency. At very high millimeter-wave frequencies where pump power is at a premium, subharmonic local oscillator pumping has numerous advantages. The devices are much easier to fabricate and the pumping power level needed is much easier to generate.
One example of a subharmonic mixer utilizing a planar doped barrier (PDB) diode is contained in U.S. Pat. No. 4,563,773, issued to Dixon, Jr. et al. A PDB diode is an effective mixing device.
The construction and operation of a planar doped barrier semiconductor device is discussed in U.S. Pat. No. 4,410,902, issued to Malik, the disclosure of which is incorporated herein by reference.
Those concerned with the development of radars into the millimeter wave region realize that pumping power (i.e., LO power) is at a premium. Subharmonic pumping at needed power levels is accomplished more simply and cheaply. There is, therefore, a continuing need for low cost mixers operating at subharmonic and lower sub-multiple frequencies with designs amenable to mass production.